Inactivation of yeast glutathione reductase by Fenton systems: effect of metal chelators, catecholamines and thiol compounds.
Oxygen radical generating systems, namely, Cu(II)/ H2O2, Cu(II)/ascorbate, Cu(II)/NAD(P)H, Cu(II)/ H2O2/catecholamine and Cu(II)/H2O2/SH-compounds irreversibly inhibited yeast glutathione reductase (GR) but Cu(II)/H2O2 enhanced the enzyme diaphorase activity. The time course of GR inactivation by Cu(II)/H2O2 dependent on Cu(II) and H2O2 concentrations and was relatively slow, as compared with the effect of Cu(II)/ascorbate. The fluorescence of the enzyme Tyr and Trp residues was modified as a result of oxidative damage. Copper chelators, catalase, bovine serum albumin and HO. scavengers prevented GR inactivation by Cu(II)/H2O2 and related systems. Cysteine, N-acetylcysteine, N-(2-dimercaptopropionylglycine and penicillamine enhanced the effect of Cu(II)/H2O2 in a concentration- and time-dependent manner. GSH, Captopril, dihydrolipoic acid and dithiotreitol also enhanced the Cu(II)/H2O2 effect, their actions involving the simultaneous operation of pro-oxidant and antioxidant reactions. GSSG and trypanothione disulfide effectively protected GR against Cu(II)/H2O2 inactivation. Thiol compounds prevented GR inactivation by the radical cation ABTS.+. GR inactivation by the systems assayed correlated with their capability for HO. radical generation. The role of amino acid residues at GR active site as targets for oxygen radicals is discussed.
Gutierrez-Correa
J
J
Bioenergetics Research Centre, School of Medicine, University of Buenos Aires, Argentina.
Stoppani
A O
AO
D002395:Catecholamines / Q000494:pharmacology*; D002614:Chelating Agents / Q000494:pharmacology*; D005609:Free Radicals; D005980:Glutathione Reductase / Q000037:antagonists & inhibitors*; D017382:Reactive Oxygen Species; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D013438:Sulfhydryl Compounds / Q000494:pharmacology*
D002395:Catecholamines; D002614:Chelating Agents; D005609:Free Radicals; D017382:Reactive Oxygen Species; D013438:Sulfhydryl Compounds; D005980:Glutathione Reductase